Harvesting heads of the above-mentioned type equip practically all harvesting machines available on the market today.
Because of the fact that the harvesting head straddles over the row of vine stocks or other shrubs, it is important that its two sub-assemblies stay as much as possible at equal distance from said vine stocks, when moving, for proper performance of the berry detaching systems. The machine operator must thus make sure that the harvesting head is always centered on the vine stock alignment.
However, it often happens that whenever the vines are low or not tied, or not very well tied, that the vegetation hanging down onto the ground is very dense and therefore partially or completely hides the vine stocks so that the operator is lacking the necessary reference points to correct the machine offset in relation to the vine row axis.
To eliminate this disadvantage, most current machines use a so-called “pendulum” guiding system actuated through the effect of gravity on the harvesting head and through the bearing of the vines onto said head.
Under this pendulum suspension system, the harvesting head is mounted on two horizontal pins, on the front and back. Such hinge pins are positioned much higher than the center of gravity of the harvesting head and in the same vertical plane in order to obtain a symmetric reaction of the pendulum consisting of said head. Guiding is achieved through the bearing reaction of the vine stocks onto the lower part of the harvesting head.
However, this pendulum guiding system currently used by most self-propelled harvesting machine builders has major disadvantages.
The major problem derived from this system results from the fact that centering is achieved through the reaction of the vine stocks on the lower guide ramps located on the lower part of the harvesting head, usually between the receiving device for the grapes and bunches stripped from the vine stocks (mobile aprons or bucket conveyors) and the ground, the distance between both parallel guide ramps making up the mechanical corridor of said harvesting head.
It is easily understood that because of the great inertia of the swinging harvesting head assembly, the reaction on the vine stocks is sometimes violent, especially at the entry of a row when the first vine stock engages into the mechanical corridor and supports by itself the reaction of the harvesting head whose the weight can be up to a mass of approximately three tons.
In addition, a pendulum system makes it necessary to provide for the lowest center of gravity in relation to the pendulum axis, which eliminates the possible mounting of the receiving bins on the swinging assembly, which would cause to add a very significant inertia when the bins are filling. In addition, the not always even filling of said bins would unbalance the pendulum, which would off-center the mechanical corridor in relation to the vine row.
It is also understood the pendulum effect triggered by gravity is also triggered by parasitic accelerations caused by the uneven contour of the ground on which the machine moves, or by the directional effects of a change of path caused by the direction of the carrier vehicle. Such parasitic accelerations are usually perpendicular to the pendulum axis, and the highly undesirable effect thereof is to trigger the guiding of the mechanical corridor but not in the right direction and to create counter-reactions on the vine stocks that may cause their breaking.
Some builders have tried to correct the above-described problem by proposing towed-type machines coupled to the tractor vehicle through an articulated drawbar or self-propelled harvesting machines with an articulated frame.